Avalanche Forecast

Issued: Mar 19th, 2014 9:32AM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Storm Slabs, Persistent Slabs and Deep Persistent Slabs.

bcorrigan, Avalanche Canada

Northwest Inland.

Summary

Confidence

Fair - Timing, track, or intensity of incoming weather system is uncertain on Friday

Weather Forecast

Synopsis: A low pressure system over northwest BC will track south eastward through BC and into Alberta.Tonight: Cloudy, trace of precipitation, freezing level at valley bottom, winds from the west, light, occasionally moderate.Thursday: Cloudy with sunny periods and flurries, trace to 10 cm of precipitation, freezing level around 700 metres, winds light, from the west.Friday: Cloudy with flurries, trace to 10 cm of precipitation, freezing level at valley bottom, light to moderate ridge top winds from the south east.Saturday: Cloudy with snow, trace to 10cm of precipitation, freezing level around 600 metres, ridge top winds, light from the south east.

Avalanche Summary

No avalanche reports from Tuesday in the region, however this is most likely as a result of poor visibility and not an indication of avalanche activity. Reports of large natural avalanche cycle during and after Mondays precipitation and wind event indicate that avalanches up to size 3, were running on the early March and Feb.10th persistent weak layers. With continued loading and wind, rider triggering is definitely possible at this time.

Snowpack Summary

10 to 20cm of overnight precipitation in some parts of the forecast region, combined with strong winds continues to build wind slabs in lee terrain and increase the depth of the storm slab that overlies the March persistent weak layer. This persistent weak layer is now buried well over a metre in most parts of the region. The recent storm snow has fallen on a melt freeze and/or rain crusts exist in most parts of the region below 1200 metres. This could become reactive on solar aspects when the sun finally comes out.The March weak layer is a combination of hard wind-scoured slab surfaces in exposed terrain, facets and/or surface hoar in sheltered and north aspects, and sun crust on steep solar aspects and is widespread throughout the forecast region.A late January/early February crust/facet/surface hoar combo is still showing up in snowpack tests with moderate to hard shear tests. This layer will be with us for a long time, and a slide triggered on this layer would be very large and destructive. Recent warming temperatures will be good for bonding on this layer, but a sudden increase in load, or a large rainfall event could "wake up" this layer and result in very large avalanches.

Problems

Storm Slabs

The recent storm snow sits on a variety of surfaces, from rain and temperature crusts at lower elevations, to wind scoured surfaces around tree line and in the alpine, with wind slabs on lee slopes. Conservative terrain choices are best right now.

Avoid freshly wind loaded features.>Use conservative route selection, stick to moderate angled terrain with low consequence.>Choose well supported terrain without convexities.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2 - 4

Persistent Slabs

The Feb. and March persistent weak layers have been re-awakened by new snow loads and might now be triggered by light loads like skiers and sledders The slab is now typically 40 to 80 cm thick and continues to produce large avalanches.

Be aware of the potential for large, deep avalanches due to the presence of buried weak layers>Be aware of thin areas that may propogate to deeper instabilites.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 4

Deep Persistent Slabs

Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.>Be aware of the potential for large, deep avalanches due to the presence of buried weak layers.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

4 - 7

Valid until: Mar 20th, 2014 2:00PM